Compared with inorganic lenses, plastic lenses have a low weight, are not easily cracked, and can be dyed, and thus have rapidly become widespread in optical elements such as eyeglass lenses and camera lenses. Thus far, a variety of resins for lenses have been developed and used, and typical examples thereof include thiourethane resins obtained from a polymerizable composition including an isocyanate compound and a thiol compound.
Plastic lenses comprised of thiourethane resins are described in Patent Documents 1 to 5 below.
Patent Documents 1 and 2 disclose polymerizable compositions obtained by mixing a polyisocyanate compound and a polythiol compound with a prepolymer that is obtained by reacting sulfur with a compound having an epithio group using an imidazole-based catalyst as a vulcanization accelerator and plastic lenses obtained from the compositions.
Patent Document 3 discloses a photosensitive resin composition including a thiourethane compound obtained from a thiol compound and an isocyanate compound, and a photopolymerization initiator such as an imidazole compound.
Patent Document 4 discloses a process for producing a polythiourethane resin in which a polythiol oligomer and a poly (thio) isocyanate group-containing compound are reacted with each other. It is disclosed that the polythiol oligomer is obtained by reacting a di- or higher-functional polythiol compound with sulfur using an imidazole-based catalyst.
Patent Document 5 discloses a polymerizable composition including (A) a compound having one or more mercapto groups, (B1) a polyurethane prepolymer and/or a polythiourethane prepolymer in which all or some of terminals are mercapto groups, and (C) a polyisocyanate compound and/or a polyisothiocyanate compound. In addition, it is described that resins can be produced by heating and polymerizing the composition in the presence of a curing catalyst such as an imidazole. However, there are no specific examples disclosed regarding the use of imidazoles.